The present invention relates to vehicle brake systems and particularly to power assist actuators for vehicle brakes.
Hydromechanical transmissions for track-laying vehicles, such as military tanks, are presently designed to provide not only propulsion and steering, but braking as well. The massive weight and the high speed capability of modern tanks represents tremendous kinetic energy which must be absorbed by the transmission service brakes. Consequently, the service brakes and their actuating system must be designed to bring the tank to a stop reliably and rapidly in response to reasonable brake actuating forces exerted by the driver. Obviously the extreme situation occurs during a panic stop from maximum speed when millions of foot-pounds of kinetic energy must be absorbed by the transmission service brakes in a matter of seconds. To achieve this, the brake actuating force manually exerted by the drive must be power assisted. The most practical source of service brake actuating power assistance is the transmission lubricating system which pumps oil under pressure to the multiplicity of gears, bearings etc., of the transmission. Thus, ideally a brake power assist unit should be of the hydraulic type. As such, it must be designed to operate effectively based on available oil pressure and supply of the transmission lubricating system.
An additional design consideration is finding available space to accept such hydraulic power assist units. In modern military tanks space external of the transmission is a premium, and it is thus preferable to locate the hydraulic power assist units within the transmission housing, particularly since they rely on the transmission lubricating system for hydraulic power. However available space within the transmission housing is also scarce. Consequently the power assist units, one for each of the right and left output transmission service brakes, must be as compact in design as possible.
In addition, it is important that the power assist units provide a force feedback to the driver in order to impart to the driver a "feel" of the service brakes during braking application. This enables the driver to better control normal deceleration either to merely reduce speed or to come to a complete, non-panic stop.
A further and extremely important design consideration is that there be a direct mechanical force coupling between the brake pedal and the transmission service brakes, such that the driver can effect reasonable deceleration and stoppage by manual effort alone should there be a loss of hydraulic fluid pressure.